Vulnerability-Lookup

GHSA-PX9F-WHJ3-246M

Vulnerability from github – Published: 2026-07-29 15:29 – Updated: 2026-07-29 15:29

Summary

Req vulnerable to multipart form-data header injection via unescaped name/filename/content_type

Details

Summary

Req's multipart form encoder interpolates the per-part name, filename, and content_type directly into the part headers without escaping. An attacker who can influence any of those values can inject CRLF-separated header lines, smuggle additional form fields, or prepend a whole extra part into the request the victim service sends downstream.

Details

Req.Utils.encode_form_part/2 in lib/req/utils.ex builds the per-part header iodata by concatenating the three caller-supplied strings verbatim into content-disposition: form-data; name="<name>"; filename="<filename>" and content-type: <content_type>. There is no CRLF stripping, no quote escaping, and no validation. A value containing "\r\n closes the surrounding quoted value and starts a new header line; an additional \r\n--<boundary> terminates the current part and lets the attacker prepend a smuggled part.

The flaw is reachable through every supported way of supplying a part. It is especially easy to hit when value is a %File.Stream{}, because filename then defaults to Path.basename(stream.path) and POSIX filenames may legitimately contain \r and \n. RFC 7578 / WHATWG form-data requires percent-encoding ", CR, and LF in these fields; the fix adopts that behavior.

PoC

Construct a malicious filename such as harmless.txt"\r\nX-Smuggled: marker\r\nContent-Disposition: form-data; name="pwned.
Call Req.post!(url, form_multipart: [upload: {"benign body", filename: <malicious>, content_type: "text/plain"}]).
The emitted multipart body contains a real X-Smuggled: header line and an extra Content-Disposition for name="pwned", alongside Req's legitimate headers.

Impact

HTTP request smuggling / multipart parameter smuggling in the HTTP client. Any application using Req to send form_multipart requests where any of name, filename, or content_type can be influenced by an untrusted source is affected, most commonly upload proxies and re-uploaders that derive filename from Path.basename/1 on a user-controlled path.

Severity

6.3 (Medium)


                  
                    CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:L/SA:N

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{
  "affected": [
    {
      "package": {
        "ecosystem": "Hex",
        "name": "req"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0.5.3"
            },
            {
              "fixed": "0.6.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-49756"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-93"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-07-29T15:29:14Z",
    "nvd_published_at": "2026-06-08T16:16:44Z",
    "severity": "MODERATE"
  },
  "details": "### Summary\n\nReq\u0027s multipart form encoder interpolates the per-part `name`, `filename`, and `content_type` directly into the part headers without escaping. An attacker who can influence any of those values can inject CRLF-separated header lines, smuggle additional form fields, or prepend a whole extra part into the request the victim service sends downstream.\n\n### Details\n\n`Req.Utils.encode_form_part/2` in `lib/req/utils.ex` builds the per-part header iodata by concatenating the three caller-supplied strings verbatim into `content-disposition: form-data; name=\"\u003cname\u003e\"; filename=\"\u003cfilename\u003e\"` and `content-type: \u003ccontent_type\u003e`. There is no CRLF stripping, no quote escaping, and no validation. A value containing `\"\\r\\n` closes the surrounding quoted value and starts a new header line; an additional `\\r\\n--\u003cboundary\u003e` terminates the current part and lets the attacker prepend a smuggled part.\n\nThe flaw is reachable through every supported way of supplying a part. It is especially easy to hit when `value` is a `%File.Stream{}`, because `filename` then defaults to `Path.basename(stream.path)` and POSIX filenames may legitimately contain `\\r` and `\\n`. RFC 7578 / WHATWG form-data requires percent-encoding `\"`, CR, and LF in these fields; the fix adopts that behavior.\n\n### PoC\n\n1. Construct a malicious `filename` such as `harmless.txt\"\\r\\nX-Smuggled: marker\\r\\nContent-Disposition: form-data; name=\"pwned`.\n2. Call `Req.post!(url, form_multipart: [upload: {\"benign body\", filename: \u003cmalicious\u003e, content_type: \"text/plain\"}])`.\n3. The emitted multipart body contains a real `X-Smuggled:` header line and an extra `Content-Disposition` for `name=\"pwned\"`, alongside Req\u0027s legitimate headers.\n\n### Impact\n\nHTTP request smuggling / multipart parameter smuggling in the HTTP client. Any application using Req to send `form_multipart` requests where any of `name`, `filename`, or `content_type` can be influenced by an untrusted source is affected, most commonly upload proxies and re-uploaders that derive `filename` from `Path.basename/1` on a user-controlled path.",
  "id": "GHSA-px9f-whj3-246m",
  "modified": "2026-07-29T15:29:15Z",
  "published": "2026-07-29T15:29:14Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/wojtekmach/req/security/advisories/GHSA-px9f-whj3-246m"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-49756"
    },
    {
      "type": "WEB",
      "url": "https://github.com/wojtekmach/req/commit/74506ff2c5addf74df85d79dc726e9b2e264a8ba"
    },
    {
      "type": "WEB",
      "url": "https://cna.erlef.org/cves/CVE-2026-49756.html"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/wojtekmach/req"
    },
    {
      "type": "WEB",
      "url": "https://github.com/wojtekmach/req/releases/tag/v0.6.0"
    },
    {
      "type": "WEB",
      "url": "https://osv.dev/vulnerability/EEF-CVE-2026-49756"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:L/SA:N",
      "type": "CVSS_V4"
    }
  ],
  "summary": "Req vulnerable to multipart form-data header injection via unescaped name/filename/content_type"
}

CVE-2026-49756 (GCVE-0-2026-49756)

Vulnerability from cvelistv5 – Published: 2026-06-08 15:20 – Updated: 2026-06-08 16:34

Title

Multipart form-data header injection in Req via unescaped name/filename/content_type

Summary

Improper Neutralization of CRLF Sequences ('CRLF Injection') vulnerability in wojtekmach Req allows multipart parameter smuggling via attacker-influenced part metadata. Req.Utils.encode_form_part/2 in lib/req/utils.ex builds the per-part headers by interpolating the caller-supplied name, filename, and content_type values directly into the content-disposition and content-type lines with no escaping or CRLF stripping. A value containing ", \r, or \n closes the surrounding quoted value and starts a new header line; an additional \r\n--<boundary> terminates the current part and prepends a smuggled part of the attacker's choosing. This is reachable through every supported way of supplying a part. It is particularly easy when value is a %File.Stream{}, because filename then defaults to Path.basename(stream.path) and POSIX filenames may legitimately contain \r and \n. Any application that forwards user-controlled filenames (or field names / MIME types) through Req.post/2 with form_multipart: lets an attacker inject arbitrary headers into the outgoing multipart body or smuggle additional fields and parts into the request the victim service sends downstream. This issue affects req: from 0.5.3 before 0.6.0.

Severity

2.1 (Low)


                        
                          CVSS:4.0/AV:L/AC:L/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:L/SI:L/SA:N

SSVC

Exploitation: poc Automatable: no Technical Impact: partial

CISA Coordinator (v2.0.3)

CWE

CWE-93 - Improper Neutralization of CRLF Sequences ('CRLF Injection')

Assigner

EEF

References

4 references

URL	Tags
https://github.com/wojtekmach/req/security/adviso…	vendor-advisoryrelated
https://cna.erlef.org/cves/CVE-2026-49756.html	related
https://osv.dev/vulnerability/EEF-CVE-2026-49756	related
https://github.com/wojtekmach/req/commit/74506ff2…	patch

Impacted products

2 products

Vendor	Product	Version
wojtekmach	req	Affected: 0.5.3 , < 0.6.0 (semver) cpe:2.3:a:wojtekmach:req::::::::
wojtekmach	req	Affected: 60253dbe9436cb8e9c738f895032f2e87939b597 , < 74506ff2c5addf74df85d79dc726e9b2e264a8ba (git) cpe:2.3:a:wojtekmach:req::::::::

Credits

Peter Ullrich Wojtek Mach Jonatan Männchen / EEF

Show details on NVD website

JSON

To clipboard

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          {
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                "id": "CVE-2026-49756",
                "options": [
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                    "Exploitation": "poc"
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                  {
                    "Automatable": "no"
                  },
                  {
                    "Technical Impact": "partial"
                  }
                ],
                "role": "CISA Coordinator",
                "timestamp": "2026-06-08T16:05:54.070488Z",
                "version": "2.0.3"
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      }
    ],
    "cna": {
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            "cpe:2.3:a:wojtekmach:req:*:*:*:*:*:*:*:*"
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          ],
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          "packageURL": "pkg:hex/req",
          "product": "req",
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            "lib/req/utils.ex"
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          "programRoutines": [
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          ],
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          "vendor": "wojtekmach",
          "versions": [
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          "collectionURL": "https://github.com",
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              "versionType": "git"
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      "cpeApplicability": [
        {
          "nodes": [
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              "cpeMatch": [
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      ],
      "descriptions": [
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          "lang": "en",
          "supportingMedia": [
            {
              "base64": false,
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              "value": "Improper Neutralization of CRLF Sequences (\u0027CRLF Injection\u0027) vulnerability in wojtekmach Req allows multipart parameter smuggling via attacker-influenced part metadata.\u003cp\u003e\u003ctt\u003e\u0027Elixir.Req.Utils\u0027:encode_form_part/2\u003c/tt\u003e in \u003ctt\u003elib/req/utils.ex\u003c/tt\u003e builds the per-part headers by interpolating the caller-supplied \u003ctt\u003ename\u003c/tt\u003e, \u003ctt\u003efilename\u003c/tt\u003e, and \u003ctt\u003econtent_type\u003c/tt\u003e values directly into the \u003ctt\u003econtent-disposition\u003c/tt\u003e and \u003ctt\u003econtent-type\u003c/tt\u003e lines with no escaping or CRLF stripping. A value containing \u003ctt\u003e\"\u003c/tt\u003e, \u003ctt\u003e\\r\u003c/tt\u003e, or \u003ctt\u003e\\n\u003c/tt\u003e closes the surrounding quoted value and starts a new header line; an additional \u003ctt\u003e\\r\\n--\u0026lt;boundary\u0026gt;\u003c/tt\u003e terminates the current part and prepends a smuggled part of the attacker\u0027s choosing.\u003c/p\u003e\u003cp\u003eThis is reachable through every supported way of supplying a part. It is particularly easy when \u003ctt\u003evalue\u003c/tt\u003e is a \u003ctt\u003e%File.Stream{}\u003c/tt\u003e, because \u003ctt\u003efilename\u003c/tt\u003e then defaults to \u003ctt\u003ePath.basename(stream.path)\u003c/tt\u003e and POSIX filenames may legitimately contain \u003ctt\u003e\\r\u003c/tt\u003e and \u003ctt\u003e\\n\u003c/tt\u003e. Any application that forwards user-controlled filenames (or field names / MIME types) through \u003ctt\u003e\u0027Elixir.Req\u0027:post/2\u003c/tt\u003e with \u003ctt\u003eform_multipart:\u003c/tt\u003e lets an attacker inject arbitrary headers into the outgoing multipart body or smuggle additional fields and parts into the request the victim service sends downstream.\u003c/p\u003e\u003cp\u003eThis issue affects req: from 0.5.3 before 0.6.0.\u003c/p\u003e"
            }
          ],
          "value": "Improper Neutralization of CRLF Sequences (\u0027CRLF Injection\u0027) vulnerability in wojtekmach Req allows multipart parameter smuggling via attacker-influenced part metadata.\n\nReq.Utils.encode_form_part/2 in lib/req/utils.ex builds the per-part headers by interpolating the caller-supplied name, filename, and content_type values directly into the content-disposition and content-type lines with no escaping or CRLF stripping. A value containing \", \\r, or \\n closes the surrounding quoted value and starts a new header line; an additional \\r\\n--\u003cboundary\u003e terminates the current part and prepends a smuggled part of the attacker\u0027s choosing.\n\nThis is reachable through every supported way of supplying a part. It is particularly easy when value is a %File.Stream{}, because filename then defaults to Path.basename(stream.path) and POSIX filenames may legitimately contain \\r and \\n. Any application that forwards user-controlled filenames (or field names / MIME types) through Req.post/2 with form_multipart: lets an attacker inject arbitrary headers into the outgoing multipart body or smuggle additional fields and parts into the request the victim service sends downstream.\n\nThis issue affects req: from 0.5.3 before 0.6.0."
        }
      ],
      "impacts": [
        {
          "capecId": "CAPEC-33",
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            {
              "lang": "en",
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              "value": "CAPEC-105 HTTP Request Splitting"
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        {
          "tags": [
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        {
          "tags": [
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      "title": "Multipart form-data header injection in Req via unescaped name/filename/content_type",
      "workarounds": [
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              "value": "\u003cp\u003eSanitize attacker-influenced \u003ctt\u003ename\u003c/tt\u003e, \u003ctt\u003efilename\u003c/tt\u003e, and \u003ctt\u003econtent_type\u003c/tt\u003e values before passing them to \u003ctt\u003e\u0027Elixir.Req\u0027:post/2\u003c/tt\u003e with \u003ctt\u003eform_multipart:\u003c/tt\u003e. At minimum, reject (or strip) any value containing \u003ctt\u003e\\r\u003c/tt\u003e, \u003ctt\u003e\\n\u003c/tt\u003e, or \u003ctt\u003e\"\u003c/tt\u003e. When forwarding uploads, derive \u003ctt\u003efilename\u003c/tt\u003e from a normalised string rather than \u003ctt\u003ePath.basename/1\u003c/tt\u003e on a user-controlled path.\u003c/p\u003e"
            }
          ],
          "value": "Sanitize attacker-influenced name, filename, and content_type values before passing them to Req.post/2 with form_multipart:. At minimum, reject (or strip) any value containing \\r, \\n, or \". When forwarding uploads, derive filename from a normalised string rather than Path.basename/1 on a user-controlled path."
        }
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      "x_generator": {
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    "assignerShortName": "EEF",
    "cveId": "CVE-2026-49756",
    "datePublished": "2026-06-08T15:20:24.035Z",
    "dateReserved": "2026-06-01T13:45:22.448Z",
    "dateUpdated": "2026-06-08T16:34:58.505Z",
    "state": "PUBLISHED"
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  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}

Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

Detection rules are retrieved from Rulezet.

The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.

Action not permitted

GHSA-PX9F-WHJ3-246M

Summary

Details

PoC

Impact

CVE-2026-49756 (GCVE-0-2026-49756)

Tags

Sightings

Nomenclature